fix: fix services accessig directly to localstorage

Prevent services accessing directly to localstorage and prefer using an astraction layer
to expose full blob. The abstraction layer (dedup services) will cover backend storage
election (local, s3, ...), encryption, etc

This change permit audio_metadata_service, media_metadaa_service, face_indexing_service to handle
blobs without worring of the backend.

note: prefered way to handle blob is the streamed way. Some services may not have this possibility

example.env

@@ -17,6 +17,17 @@ OXICLOUD_STORAGE_PATH=./storage
 # Path to static files directory (default: ./static)
 OXICLOUD_STATIC_PATH=./static
 
+# Directory for tier-1 temporary data — pure scratch, safe to lose at reboot.
+# Services that need a filesystem path (audio ID3/MP3 duration, video EXIF via
+# ffprobe/nom-exif, etc.) stream blobs here from the active backend before
+# handing the path to the extractor. The file is auto-removed after each use.
+#
+# Default: system tempdir (`std::env::temp_dir()`, honours $TMPDIR / $TMP).
+# On Linux `/tmp` is often mounted as tmpfs (RAM-backed); high-concurrency
+# production deployments concerned about RAM should point this at a
+# disk-backed dir (e.g. /var/lib/oxicloud/tmp).
+#OXICLOUD_TEMP_DIR=/var/lib/oxicloud/tmp
+
 # Server port (default: 8086)
 OXICLOUD_SERVER_PORT=8086